The present invention relates in general to load distribution arrangements which are designed to distribute the force at one location over a larger area. Included within the broad class of load distribution arrangements are those designs which transfer a loading or clamping force from one location to another. This other location may represent a more central portion of an object, such as a fuel injector body. U.S. Pat. No. 5,503,128, issued Apr. 2, 1996 to Hickey et al. is one example of this type of arrangement. Other examples of load distribution arrangements can be found in U.S. Pat. No. 5,697,345, issued Dec. 16, 1997 to Genter, and in U.S. Pat. No. 5,706,786, issued Jan. 13, 1998 to Stephanus et al.
In each of these three patents the corresponding load distribution arrangement includes the addition of a separate component which is assembled into the existing structure. While still being quite beneficial to the overall assembly, the fabrication and assembly of this separate component represents an added cost with added labor required in order to perform the necessary disassembly and assembly steps to incorporate this additional component.
Not all load distribution arrangements require the assembly or integration of a separate component. It is possible, and in the right circumstances may be preferred, to incorporate the structure(s) required for load distribution or force transferring directly into an existing component. U.S. Pat. No. 5,873,331, issued Feb. 23, 1999 to Jutz, discloses one such arrangement for transmitting a force from one location to another where the specific feature is incorporated into an existing component. In the case of U.S. Pat. No. 5,873,331, this existing component is a cylinder head casting for a multi-cylinder internal combustion engine. The incorporated feature is a series of walls that connect the bolt mounting columns. The xe2x80x9cfour cornersxe2x80x9d arrangement of the bolt mounting columns results in a total of four walls boxing in each cylindrical combustion chamber.
If we focus this discussion on multi-cylinder internal combustion engines, it will be appreciated that the generally cylindrical combustion chamber needs to be sealed so that the efficiency of the combustion process is not compromised. While a xe2x80x9cperfectxe2x80x9d seal may not be possible in view of the numerous interfaces which are subject to leakage and the operating stresses which are generated during the combustion process, there is a continuing desire to perfect the seal as much as possible.
Cylinder heads, specifically the combustion decks, have traditionally had problems sealing combustion gas within the cylinder, especially in between the head anchoring bolts whenever there is a long span between bolts. Problems sealing combustion gas also occur in those designs where there is low bending stiffness in the mating components. The primary reason for these problems in sealing is that it is difficult to distribute the bolt load uniformly around the combustion seal. The current problem, and the concerns over combustion gas sealing, will likely become even greater as diesel engines go to higher cylinder pressures for performance and emissions considerations. Part of the challenge is due to the current configuration which includes locating the attachment bolts for the combustion deck at what could be described as fixed points or discrete locations. Typically four or more (eight maximum) bolts are used for each cylinder. This means that a circular interface is being sealed (or at least is trying to be sealed) by the use of four to eight bolts placed at discrete locations around each cylinder. The four-walls design of the Jutz patent only accents the mismatch of geometric shapes. The box-like arrangement is not shaped so as to extend uniformly around the entire circular interface for each cylinder. The result is that portions of the box-like frame of Jutz are closer to the circular edge and other portions are farther apart, contributing to a condition of non-uniformity. The raised walls of Jutz also represent an inefficiency in that there are more significant material costs and added weight with this design. Additional bolts may be positioned around the perimeter of the cylinder, but even with this addition, significant fluctuations in sealing load will occur.
As for other possibilities for addressing the need for improved sealing around the cylinder in order to hold in all of the combustion gas, simply making the combustion deck of the head thicker can help the sealing problem, but this approach introduces high thermal stresses which generally compromise head durability. The typical option which is employed is to increase the bolt loading, but that increases the bolt and bolt bore sizes, resulting in a higher cost and a heavier product. Further, this option is not always effective in correcting or fixing any combustion gas leakage. Another option which might be considered is to reduce the span between the bolts. However, the longest bolt span is typically governed by the bore size and the spacing between cylinders. Accordingly, very little can be done to actually reduce the longest span between bolts.
In order to address what are believed to be shortcomings and limitations with earlier designs and in order to improve upon the sealing efficiency, the present invention was conceived. The present invention provides a circular back up rib on the coolant side of the combustion deck. This circular back up rib is positioned very near to the combustion seal and extends to intersect the head bolt bosses. This rib helps to distribute the bolt loading (typically applied at four to eight discrete locations around the perimeter of each cylinder) more evenly over and more uniformly around the combustion seal. The rib also provides a more uniform stiffness over the circumferential area of the seal. Additionally, the rib offers more surface area (for the head) directly in contact with coolant, allowing the head to run cooler. By reducing the head operating temperature, the corresponding or resulting thermal stresses are reduced. The rib also reduces the deflections due to cylinder pressure loads, thus reducing the stresses and strains which are seen by the cylinder head.
The arrangement contemplated by the present invention accomplishes its various improvements in a manner and by a structure which are novel and unobvious.
A unitary combustion deck for an internal combustion engine having at least one cylinder according to one embodiment of the present invention includes a main body portion having a cylinder-facing surface and a coolant-side surface, a plurality of bolt bosses integral with the coolant-side surface, each bolt boss of this plurality defining a bolt-receiving aperture which extends through the main body portion and a load distribution rib constructed and arranged to extend in a ring-like form around the cylinder while integrally interconnecting with each bolt boss of the plurality of bolt bosses.
One object of the present invention is to provide an improved combustion deck for an internal combustion engine.
Related objects and advantages of the present invention will be apparent from the following description.